Various Clients utilizing Shopify required a flexible solution for rewarding higher-value purchases based on price thresholds. Existing apps on the marketplace (at the time) were either too bloated and expensive or too simplistic to match specific business needs. To solve this, I developed a lightweight JavaScript widget that dynamically injected custom reactive progress bars directly into merchant themes. I paired this custom widget with a Node.js application that handled automated script injection upon installation. Engineering this as a completely self-contained and theme-agnostic component required ensuring the vanilla JavaScript logic could seamlessly execute across various legacy and modern Shopify layouts without causing performance degradation. The implementation successfully replaced heavy third-party software and provided a tailored alternative that directly contributed to an approximate 15% lift in average order value (AOV) for participating clients.